The team gave cognitive tests to 40 patients with MS and 40 healthy control subjects over the course of a year. People with MS scored 70% higher on cooler days than warmer ones, while temperature did not correlate to cognitive performance in the healthy control subjects.

These findings could affect the way researchers look at data from clinical trials of people with MS. Many trials run for at least six months, spanning multiple seasons. Differences in outdoor temperature could confound comparisons between cognitive tests taken at the beginning and end of the trials.